JP2011528173A - Illumination system of microlithographic projection exposure apparatus - Google Patents

Abstract

The illumination system of the microlithographic projection exposure apparatus (10) includes an optical raster element (72) configured to generate a plurality of secondary light sources (95) located in the system pupil plane (70). The optical raster element (72) has a plurality of light incident facets (92) each associated with one of the secondary light sources (95). The beam deflection device includes a beam deflection array (46) of reflective or transmissive beam deflection elements (M _ij ), each of the beam deflection elements being produced by a deflection angle produced by these beam deflection elements (M _ij ). Is configured to illuminate a spot (90) on one of the light incident facets (92) at a position that is variable by changing. The control unit (50) is capable of forming a variable light pattern (LP) organized from the spots (80) on at least one of the plurality of light incident facets (92) so that the beam deflection element (M) _ij ) is configured to control.
[Selection] Figure 6

Description

  In general, the invention relates to an illumination system for illuminating a mask in a microlithographic exposure apparatus, and in particular to such a system including a mirror array or other beam deflection element. The invention also relates to a method of operating such a system.

  Microlithography (also called photolithography or simply lithography) is a technique for the fabrication of integrated circuits, liquid crystal displays, and other microstructured devices. The microlithographic process is used to pattern features in a thin film stack formed on a substrate, eg, a silicon wafer, in the context of an etching process. In each level of fabrication, the wafer is first coated with a photoresist, which is a radiation sensitive material such as deep ultraviolet (DUV) light. Next, the wafer having the photoresist on the top is exposed to projection light in a projection exposure apparatus. The apparatus projects a mask containing a pattern onto the photoresist such that the photoresist is exposed only at certain locations determined by the mask pattern. After exposure, the photoresist is developed to produce an image corresponding to the mask pattern. An etching process then transfers this pattern to the thin film stack on the wafer. Finally, the photoresist is removed. Repeating this process with different masks results in a multilayer microstructured component.

  In general, a projection exposure apparatus includes an illumination system for illuminating a mask, a mask stage for aligning the mask, a projection objective, and a wafer alignment stage for aligning the photoresist-coated wafer. The illumination system illuminates a field of view on the mask that may have the shape of, for example, a rectangular slit or a curved slit.

  In current projection exposure apparatus, a distinction can be made between two different types of apparatus. In one type, each target portion on the wafer is irradiated by exposing the entire mask pattern onto the target portion at once. Such an apparatus is commonly referred to as a wafer stepper. In the other type of device, commonly referred to as a step-and-scan device or scanner, each target portion progressively scans the mask pattern along the scanning direction under the projection beam while simultaneously scanning the substrate in this direction. Irradiation is performed by moving in parallel or anti-parallel. The ratio of the speed of the wafer to the speed of the mask is usually less than 1 and equal to the magnification of the projection objective, for example 1: 4.

  It should be understood that the term “mask” (or reticle) should be interpreted broadly as a patterning means. In general, the mask used includes a transmissive or reflective pattern and can be, for example, of binary type, alternating phase shift type, attenuated phase shift type, or various hybrid mask types. However, there are also active masks, for example masks achieved as programmable mirror arrays. Similarly, a programmable LCD array can be used as an active mask.

  As technology for manufacturing microstructured devices advances, there is an ever increasing demand for illumination systems. Ideally, the illumination system illuminates each point of the illumination field on the mask with projection light having a well-defined irradiance and angular distribution. The term angular distribution describes how the total light energy of a light beam that converges for a particular point in the mask plane is distributed among the various directions of the light rays that make up the light beam.

  The angular distribution of the projection light incident on the mask is usually adapted to the type of pattern projected on the photoresist. For example, a relatively large sized feature may require a different angular distribution than a small sized feature. The most commonly used angular distributions of projection light are called conventional illumination settings, annular illumination settings, dipole illumination settings, and quadrupole illumination settings. These terms mean the irradiance distribution in the system pupil plane of the illumination system. For example, in the annular illumination setting, only the annular region in the system pupil plane is illuminated. In this case, there is only a small angle range in the angular distribution of the projection light, and therefore all the light rays are incident on the mask at a similar angle.

  Various means are known in the art for modifying the angular distribution of the projection light in the mask plane in order to obtain the desired illumination setting. In the simplest case, a diaphragm containing one or more apertures is positioned on the pupil plane of the illumination system. Since the position in the pupil plane is converted to an angle in a Fourier-related field plane such as the mask plane, the size, shape, and position of the aperture in the system pupil plane determine the angular distribution in the mask plane. However, any change in lighting settings requires a change of aperture. Adjusting the lighting settings will require a very large number of apertures with apertures having slightly different sizes, shapes, or positions, so the above will make it difficult to finally adjust the lighting settings. Become.

  Thus, many common illumination systems include adjustable elements that allow the pupil plane illumination to be continuously changed, at least over a certain range. Conventionally, a zoom axicon system including a zoom objective system and an axicon element pair is used for this purpose. Axicon elements are refractive lenses that have a conical surface on one side and are usually flat on the opposite side. By providing a pair of such elements, one having a conical convex surface and the other having a complementary conical concave surface, the light energy can be shifted radially. This shift is a function of the distance between the axicon elements. The zoom objective makes it possible to change the size of the illumination area in the pupil plane.

  In order to further enhance the flexibility of generating different angular distributions in the mask plane, it has been proposed to use a mirror array that illuminates the pupil plane.

  In EP 1 262 836 A1, the mirror array is achieved as a microelectromechanical system (MEMS) comprising more than 1000 fine mirrors. Each of the mirrors can be tilted in two different planes perpendicular to each other. Accordingly, radiation incident on such a mirror device can be reflected in (desirably) any desired direction of the hemisphere. A condenser lens disposed between the mirror array and the pupil plane converts the reflection angle generated by the mirror into a position in the pupil plane. This known illumination system makes it possible to illuminate the pupil plane with a plurality of circular spots, each associated with one specific fine mirror and tiltable to freely move across the pupil plane To do.

  Similar illumination systems are known from US 2006/0087634 A1, US 7,061,582 B2, and WO 2005/026843 A2.

  The geometry of the field illuminated in the mask plane is usually determined by a number of components. One of the most important components in this regard is an optical raster element that generates multiple secondary light sources in the system pupil plane. The angular distribution of the luminous flux emitted by the secondary light source is directly related to the geometry of the field of view illuminated in the mask plane. By properly determining the optical properties of the optical raster element, eg, the refractive power in the orthogonal direction, the desired field geometry can be obtained.

  In general, it is desirable that the geometry of the illumination field can be changed at least within a certain range. Since the optical properties of the optical raster element cannot be easily changed, a field stop is provided which is imaged on the mask by the field stop objective. The field stop typically includes a plurality of blades that can be individually moved to form the boundaries of the illuminated field within the mask. The field stop also ensures a sharp edge of the illumination field. In scanner-type devices, an adjustable field stop is required to open and close the illumination field at the beginning and end of each scanning process.

  If the illumination field geometry is changed using an adjustable field stop, light loss is inevitable because a portion of the projection light is shielded by the field stop blades.

EP 1 262 836 A1 US 2006/0087634 A1 US 7,061,582 B2 WO 2005/026843 A2 WO 2005/075522 A US 2004/0036977 A1 US 2005/0018294 A1

  The object of the present invention is to provide an illumination system that makes it possible to change the geometry of the illumination field with less light loss.

  According to the present invention, the above object is achieved by an illumination system comprising a primary light source, a system pupil plane, and a mask plane on which an illuminated mask can be placed. The illumination system further includes an optical raster element configured to generate a plurality of secondary light sources located in the system pupil plane. The optical raster element has a plurality of light incident facets each associated with one of the secondary light sources. The beam deflection device of the illumination system includes a beam deflection array of reflective or transmissive beam deflection elements. Each beam deflection element is configured to illuminate a spot on one of the light incident facets at a position that is variable by changing the deflection angle produced by these beam deflection elements. The control unit is configured to control the beam deflection element so that a variable light pattern organized from the spots can be formed on at least one of the plurality of light incident facets.

  The present invention takes advantage of the fact that the position of the optical raster element on the light facet is converted to the angle of light emitted by the secondary light source. Thus, each light pattern illuminated on a facet is associated with a different angular distribution of light emitted by a secondary light source associated with this light incident facet. The angular distribution of the secondary light source is converted back into the illumination field geometry in the mask plane, so that the light pattern illuminated on the light incident facet is relative to the illumination field geometry in the mask plane. There is a one-to-one correspondence. In the absence of optical aberrations, the illumination field is an overlay of images of the light pattern formed on the light entrance facets of the optical raster element.

  The provision of the beam deflection device makes it possible to accurately change the position of the spot illuminated on the light entrance facet of the optical raster element. In order to generate a different light pattern, it is only necessary that the spot illuminated by the beam deflection element is illuminated by a beam deflection element having a total area sufficiently smaller than the maximum total area of the light incident facets. Preferably, the spot area is at least 5 times, more preferably at least 10 times, and most preferably at least 20 times smaller than any of the above-mentioned maximum total areas of the light incident facets.

  In contrast to prior art illumination systems that include a beam deflection device in which the spot is determined to illuminate at least a substantially complete area of the light incident facet, the substantially small spot size (facet area) of the present invention. Makes it possible to generate a kind of illumination microstructure in which the illumination field geometry is encoded on the optical raster element.

  By changing this microstructure, the illumination field geometry can be changed without incurring substantial light loss, as is the case when an adjustable field stop is used for this purpose. Furthermore, it is possible to completely eliminate the field stop and also to completely omit the field stop objective, which greatly simplifies the overall layout of the illumination system. Nevertheless, if a field stop is provided, the various geometries will be determined mainly by the beam deflection device, whereas the field stop guarantees a sharp edge exclusively and is projected. Only a small part of the light is shielded.

  The spot illuminated on the light incident facet by the beam deflection element can have any arbitrary geometry. These geometric shapes may not be equal in all spots. For example, rectangular spots having different spot sizes, or a combination of rectangular spots and triangular spots can be considered. Preferably, the spots have a geometric shape that can be organized into large areas so that no gaps remain between adjacent spots, or very little gaps remain. Usually, the geometry of the spot illuminated on the light entrance facet mainly depends on the angular distribution of the light incident on the micromirror. A microlens array placed in front of the micromirror can be used to generate an angular distribution that yields the desired spot geometry.

  In one embodiment, the spot has at least a substantially rectangular geometry. This rectangular geometry allows such spots to be aligned along columns, and then (following) combining these columns into larger rectangular areas that are illuminated on a single light incident facet. It is advantageous because it can be done.

  Usually, it is preferable if the light patterns generated on all illuminated light incident facets at a given moment are equal. This ensures that all secondary light sources illuminate the same field in the mask plane so that the intensity is at least substantially equal across the illumination field. However, in other cases it may be desirable to have a constant intensity profile that is within the illumination field. For example, in some scanner type projection exposure apparatus, it is desirable to have an intensity profile that has an intensity that increases and decreases smoothly at an edge extending perpendicular to the scanning direction of the apparatus. In this case, there should be a different light pattern on the light incident facet that is illuminated at a given moment.

  In one embodiment, the length of the light pattern along the scanning direction is gradually changed during the scanning process of the apparatus, whereas the length of the light pattern along the direction perpendicular to the scanning direction is constant. The control unit is configured to control the beam deflection element. This configuration can be used to mimic the function of a field stop that can be adjusted at the start and end of each scanning process.

  When a pulsed laser is used as the primary light source in the illumination system, the change in the light pattern must be synchronized with the laser pulse repetition rate.

  Such synchronization may not be necessary if a light shield is provided on at least some of the light incident facets. The provision of these light shields allows the light incident pattern to be moved continuously across the light incident facets so that the light shield gradually blocks more of the spots. In addition, this results in a gradual reduction in the size of the light pattern and thus in the field of view illuminated in the mask plane.

  In this connection, it can be considered that at least one light incident facet is provided with a pair of light blocking bodies arranged on opposite sides of the light incident facet. Such a configuration is particularly advantageous when the illumination field should be amplified and reduced along the scanning direction at the beginning and end of the scanning process, respectively.

  According to another embodiment, the illumination system includes a diaphragm disposed proximate to the beam deflection device. An actuator is provided to move the diaphragm parallel to the scanning direction of the microlithographic projection exposure apparatus. As the diaphragm moves continuously or intermittently within the beam associated with the beam deflection element, the increased or decreased portion of these beams will be shielded by the diaphragm. For example, if a light beam that initially only contributes to illumination of a certain area in the field illuminated on the mask is blocked, this area will become dark when the diaphragm begins to move. In one embodiment, this area is a line extending perpendicular to the scan direction so that the movement of the diaphragm results in the general field geometry changes required at the beginning and end of each scan process. .

  The beam deflection element can be configured as a mirror that can be tilted by two tilt axes forming an angle therebetween. In another embodiment, the beam deflection element is an electro-optic element or an acousto-optic element.

  According to the present invention, the above mentioned objects relating to the method are: a) providing an illumination system of a microlithographic projection exposure apparatus comprising an optical raster element having a plurality of light incident facets; b) a light pattern organized from individual spots. Generating on the light incident facet of the optical raster element, c) determining that the geometry of the field of view illuminated in the mask plane should be changed, d) rearranging the spots, and / or Or by removing and / or adding to altering the light pattern on the light incident facet.

  The description given above with respect to the illumination system according to the invention also applies when necessary changes are made.

  The various features and advantages of the present invention may be more readily understood by reference to the following detailed description, taken in conjunction with the accompanying drawings, in which:

1 is a very simple perspective view of a projection exposure apparatus according to the present invention. FIG. 2 is a meridional section through an illumination system housed in the projection exposure apparatus shown in FIG. 1. FIG. 3 is a perspective view of a mirror array included in the illumination system of FIG. 2. FIG. 4 is an enlarged excerpt of FIG. 2 showing the mirror array of FIG. 3 and the first microlens of the optical raster element. FIG. 3 is an enlarged excerpt of FIG. 2 showing the first and second microlenses and the condenser lens of the optical raster element. It is a top view on the system pupil surface where the secondary light source was formed. FIG. 6 is a top view on an optical raster element having a portion of light incident facets illuminated by a rectangular light pattern. FIG. 6 is a top view on a single light incident facet illuminated by a rectangular light pattern. FIG. 8 is a series of top views on the light incident facets shown in FIG. 7 illuminated with different light patterns at the start of the scanning process. FIG. 8 is a series of top views of the light incident facets shown in FIG. 7 illuminated with different light patterns at the end of the scanning process. FIG. 6 is a top view on three adjacent light incident facets illuminated with different light patterns. FIG. 6 is a schematic diagram showing an intensity profile of an illumination field along a scanning direction. FIG. 6 is a schematic diagram showing an intensity profile of an illumination field along a scanning direction. FIG. 6 is a schematic diagram showing an intensity profile of an illumination field along a scanning direction. FIG. 6 is a schematic diagram showing an intensity profile of an illumination field along a scanning direction. FIG. 4 is a top view on an optical raster element with different numbers of light facets illuminated with different light patterns. FIG. 4 is a top view on an optical raster element with different numbers of light facets illuminated with different light patterns. FIG. 4 is a top view on an optical raster element with different numbers of light facets illuminated with different light patterns. FIG. 5 is a partially perspective view of a mirror array, a condenser, and first and second microlenses of an optical raster element when the diaphragm begins to move into the optical path. 2 is a flowchart of a method for operating an illumination system of a microlithographic projection exposure apparatus according to the present invention;

I. General Structure of Projection Exposure Apparatus FIG. 1 is a very simple perspective view of a projection exposure apparatus 10 including an illumination system 12 for generating a projection light beam. The projection light beam illuminates the field of view 14 on the mask 16 containing the microstructures 18. In this embodiment, the illumination field 14 has a generally ring segment shape. However, other, for example, rectangular illumination fields 14 are also contemplated.

  The projection objective 20 images the structure 18 in the illumination field 14 onto a photosensitive layer 22, for example a photoresist, deposited on a substrate 24. A substrate 24, which can be formed by a silicon wafer, is placed on a wafer stage (not shown) such that the upper surface of the photosensitive layer 22 is exactly located in the image plane of the projection objective 20. The mask 16 is positioned in the object plane of the projection objective 20 using a mask table (not shown). Since the projection objective 20 has a magnification smaller than 1, a reduced image 14 ′ of the structure 18 in the illumination field 14 is projected onto the photosensitive layer 22.

  During projection, the mask 16 and the substrate 24 move along a scanning direction that coincides with the Y direction. Thus, the illuminated field 14 is scanned across the mask 16 so that a structured area larger than the illuminated field 14 can be continuously projected. In many cases, this type of projection exposure apparatus is referred to as a “step and scan apparatus” or simply a “scanner”. The ratio between the speed of the mask 16 and the speed of the substrate 24 is equal to the magnification of the projection objective 20. When the projection objective 20 inverts the image, the mask 16 and the substrate 24 move in opposite directions as indicated by arrows A1 and A2 in FIG. However, the present invention can also be used for stepper tools where the mask 16 and substrate 24 do not move during mask projection.

  In the illustrated embodiment, the illumination field 14 is not centered with respect to the optical axis 26 of the projection objective 20. Such a modified illumination field 14 may be necessary in certain types of projection objectives 20. In other embodiments, the illumination field 14 is centered with respect to the optical axis 26.

II. General Structure of Illumination System FIG. 2 is a more detailed meridional section through the illumination system 12 shown in FIG. For purposes of clarity, the illustration of FIG. 2 is greatly simplified and is not to scale. This means in particular that different optical units are represented by only a few optical elements. In reality, these units can include a significant number of lenses and other optical elements.

  The illumination system 12 includes a housing 28 and a light source that is achieved as an excimer laser 30 in the illustrated embodiment. Excimer laser 30 emits projection light having a wavelength of about 193 nm. Other types of light sources and other wavelengths such as 248 nm or 157 nm are also contemplated.

  In the illustrated embodiment, the projection light emitted by the excimer laser 30 enters a beam expansion unit 32 where the light beam is expanded without changing the geometrical luminous flux. The beam expansion unit 32 can include several lenses, for example as shown in FIG. 2, or can be achieved as a mirror array. The projection light exits from the beam expanding unit 32 as a substantially parallel beam 34. In other embodiments, the beam can have a significant divergence. The parallel beam 34 is incident on a plane folding mirror 36 provided to reduce the overall size of the illumination system 12.

After reflection from the folding mirror 36, the beam 34 is incident on the array 38 of microlenses 40. A mirror array 46 is disposed in or near the rear focal plane of the microlens 40. As will be described in more detail below, the mirror array 46 preferably includes a plurality of small individual mirror elements M _ij that can be tilted independently of each other by two tilt axes aligned perpendicular to each other. The total number of mirror elements M _ij can be greater than 100 or even greater than a few thousand. The reflective surface of the mirror element M _ij can be flat, but can be curved if additional power is desired. Apart from that, a diffractive structure can be provided on the mirror surface. In this embodiment, the number of mirror elements M _ij is equal to the number of microlenses 40 included in the microlens array 38. Accordingly, each microlens 40 guides the converged light beam onto one mirror element M _ij of the mirror array 46.

The tilt movement of the individual mirror element M _ij is controlled by a mirror control unit 50 connected to the overall system controller 52 of the illumination system 12. The actuator used to set the desired tilt angle of the mirror element M _ij is such that each individual mirror element M _ij can reflect incident light with a reflection angle that can be changed in response to a control signal. A control signal is received from the mirror control unit 50. In the illustrated embodiment, there is a continuous tilt angle range in which the individual mirror elements M _ij can be arranged. In other embodiments, the actuator is configured such that only a limited number of discrete tilt angles can be set.

FIG. 3 is a perspective view of a mirror array 46 including only _8.8 = 64 mirror elements M _ij for the sake of simplicity. The light beam 54a incident on the mirror array 46 is reflected in different directions depending on the tilt angle of the mirror element _Mij . In this schematic diagram, a particular mirror element M ₃₅ is relative to another mirror element M ₇₇ so that the light beams 54b, 54b ′ reflected by the mirror elements M ₃₅ and M ₇₇ are reflected in different directions. It is assumed that it is inclined around two inclination angles 56x, 56y.

  The mirror array 46 is replaced by any other deflecting structure that allows light incident on the structure to be directed in various directions that can be individually changed in different structural parts under application of appropriate control signals. can do. Such another structure can include, for example, an electro-optic element or an acousto-optic element. For such elements, the refractive index can be altered by exposing the appropriate material to ultrasound or an electric field, respectively. These effects can be used to produce a refractive index grating that guides incident light in various directions.

Referring again to FIG. 2, the light beam reflected from the mirror element M _ij is incident on the first condenser 58, and the condenser 58 causes the slightly diverging light beam to be at least substantially on the optical integrator 72 at this point. The optical integrator 72 generates a plurality of secondary light sources. The optical integrator 72 expands the range of angles formed between the light beam and the optical axis OA of the illumination system 12. In other embodiments, the first condenser 58 is omitted so that the light beam incident on the optical integrator 72 has a large divergence.

  In the illustrated embodiment, the optical integrator 72 is achieved as a fly-eye lens that includes two substrates 74, 76 that each include two orthogonal arrays of parallel cylindrical microlenses. Other configurations of optical integrators are also contemplated, such as integrators that include an array of microlenses that have rotationally symmetric surfaces but have rectangular boundaries. See WO 2005/075522 A, US 2004/0036977 A1, and US 2005/0018294 A1, where various types of optical integrators suitable for illumination system 12 are described. The function of the optical integrator 72 will be described in more detail below with reference to FIGS. 5a and 5b.

  Reference numeral 70 represents the system pupil plane of the illumination system 12 that substantially forms the angular distribution of light incident on the mask 14. The system pupil plane 70 is usually a flat surface or a slightly curved surface, and is arranged in or near the optical integrator 72. Since the angular light distribution in the system pupil plane 70 is directly converted into an intensity distribution in the subsequent field plane, the optical integrator 72 substantially reduces the basic geometry of the illumination field 14 on the mask 16. Decide. Since the optical integrator 72 expands the angular range larger in the X direction than in the scanning direction Y, the illumination field 14 has a larger dimension along the X direction than along the scanning direction Y.

  The projection light emitted from the secondary light source generated by the optical integrator 72 is incident on a second condenser 78 represented by only a single lens in FIG. 2 for the sake of simplicity. The second condenser 78 ensures a Fourier relationship between the system pupil plane 70 and the subsequent intermediate field plane 80 where the field stop 82 is located. The second condenser 78 superimposes the light flux generated by the secondary light source in the intermediate field plane 80, thereby providing a very uniform illumination of the intermediate field plane 80.

  The field stop 82 can include a plurality of movable blades to ensure a sharp edge of the illumination field 14 on the mask 16. The blade moves not only when a new mask with different dimensions is projected, but also at the beginning and end of each scanning process to ensure that each point on the mask 16 receives the same amount of light energy. Is done.

  The field stop objective 84 provides optical conjugate between the intermediate field plane 80 and the mask plane 86 on which the mask 16 is disposed. Therefore, the field stop 82 is clearly imaged on the mask 16 by the field stop objective system 84. As will be described below, the field stop 82 and the field stop objective 84 can be omitted in other embodiments.

III. Illumination System Functions and Controls FIG. 4 is an excerpt of FIG. 2 showing the first microlens 88 formed on the first substrate 74 of the mirror array 46, the first condenser 58, and the optical integrator 72. . In this embodiment, the microlens 88 is rotationally symmetric but has a square border. In other embodiments, each microlens is formed of two intersecting cylindrical microlenses.

As illustrated in FIG. 4, each mirror element M _ij generates a light beam L _ij that illuminates a small spot on one light incident facet 92 of the first microlens 88. The position of the spot can be changed by tilting the mirror element M _ij . The geometry of the spot 90 depends in particular on the optical properties of the microlenses 40 of the array 38 and the optical properties of the mirror elements M _ij . In some embodiments, the geometry of the spot 90 is circular, and in other embodiments described below, the geometry is generally rectangular, and in particular, square.

As can be seen in FIG. 4, the diameter D of the spot 90 is smaller than the diameter of the entrance facet 92 of the illuminated first microlens 88. In general, the total area of each spot 90 illuminated on the light incident facet 92 of the first microlens 88 is significantly smaller than the area of the respective light incident facet 92, for example at least 5 times, preferably , At least 10 times, more preferably at least 20 times smaller. If the light incident facets 92 have different areas and each spot 90 can be generated on any of these facets, the maximum area of the light incident facets 92 can be referenced. If the spot 90 is sufficiently small compared to the light incident facet 92 of the first microlens 88, a different light pattern can be generated on the light incident facet 92. The light pattern can be easily changed by appropriately controlling the mirror element M _ij using the mirror control unit 50.

  With reference to FIG. 5a, the effect produced by illuminating different light patterns on the light incident facet 92 will be described. This figure is an enlarged excerpt of FIG. 2 showing the optical integrator 72, the second condenser 78, and the intermediate field plane 80, and is not to scale. For simplicity, only two pairs of first microlens 88 and second microlens 94 are shown from optical integrator 72. As described above, the microlenses 88, 94, sometimes referred to as field honeycomb lenses and pupil honeycomb lenses, are shown as individual microlenses having, for example, rotationally symmetric reflective surfaces and rectangular boundaries, or in FIG. As shown, it can be configured as a crossed cylindrical microlens. The microlenses 88 and 94 need only have non-zero refractive power along at least one direction perpendicular to the optical axis OA of the illumination system 12.

Each pair of adjacent microlenses 88, 94 generates a secondary light source. In the upper half of FIG. 5a, the convergent light beams L _1a , L _2a , and L _3a illustrated by the solid line, the dotted line, and the broken line respectively are incident on different points of the light incident facet 92 of the first microlens 88. Assumes. After passing through the two microlenses 88 and 94 and the condenser 78, the light beams L _1a , L _2a , and L _3a converge to the focal points F ₁ , F ₂ , and F ₃ , respectively. Thus, from the upper half of FIG. 5a, there is a pair between a position where the light ray is incident on the light incident facet 92 and a position where this light ray passes through the intermediate field plane 80 (or any other conjugate field plane). It becomes clear that there is one correspondence. As a result, by changing the area illuminated on the light incident facet of the first microlens 88, the field illuminated in the intermediate field plane 80 (and thus the field 14 illuminated in the mask plane 86). The dimensions can be changed. This region can be changed very effectively using the mirror device 46 described above with reference to FIG.

  Of course, these considerations apply separately for the X and Y directions. Therefore, by changing the illumination of the light incident facet 92 separately in the X direction and the Y direction, the geometric shape of the illumination field 14 can be independently changed in the X direction and the Y direction. In other words, if the area illuminated on the light incident facet 92 of the first microlens 88 is properly determined, an illumination field of almost any arbitrary geometry in the intermediate field plane 80 can be obtained. .

The lower half of FIG. 5a shows the case where the parallel beams L _1b , L _2b and L _3b are incident on different areas of the light entrance facet 92 of the first microlens 88. The luminous flux is focused at a common focal point F located in the second microlens 94 and then passes through the intermediate field plane 80 in parallel as before at this point. As described above, it can be seen that the regions where the light beams L _1b , L _2b , and L _3b are incident on the light incident facet 92 are converted into regions illuminated in the intermediate field plane.

In FIG. 5 a, it is assumed that the system pupil plane 70 is positioned immediately after the second microlens 94. As illustrated in the upper half of FIG. 5 a, in the case of the strongly converging light beams L _1a , L _2a , and L _3a , the light beams L _1a , L _2a , and L _3a are applied to the second microlens 94. Intersects with the system pupil plane 70 in an area slightly larger than the exit facet. As illustrated in the lower half of FIG. 5 a, in the case of parallel beams L _1a , L _2a , and L _3a , the beams L _1b , L _2b , and L _3b are emitted from the second microlens 94. Intersects with the system pupil plane 70 in an area significantly smaller than the facet. In many cases, light incident on the optical integrator 72 is slightly divergent, which is somewhere between what is shown in the upper half and what is shown in the lower half of FIG. This corresponds to the illumination state on the light incident facet 92. In such a case, the secondary light source may have a geometric shape as shown in FIG. 5 b, which is a top view on the system pupil plane 70. The secondary light source is indicated by a square 95, and a circle 97 indicates the effective diameter of the system pupil plane. In order to obtain an illumination field having an aspect ratio different from 1, the light emitted from each secondary light source 95 will typically have a different divergence along the X and Y directions.

  In the above description, it is assumed that all the first micro lenses 88 are illuminated in the same manner so that the fields of view illuminated by the secondary light source 95 overlap. If the intensity in the illumination field is not constant and should have a certain distribution along at least one direction, the light incident facets 92 of the first microlens 88 can be illuminated differently.

  Depending on the geometry of the spot 90, it may not be possible to illuminate the continuous area with a constant irradiance on the light incident facet 92 of the first microlens 88. For example, if the spot has a circular geometry, the light incident facet 92 is such that either a (small) gap remains between adjacent spots 90 or the spots 90 partially overlap. These spots can be placed on top. For this reason, in the following, the area illuminated on the light incident facet will be referred to as a light pattern that may or may not include a gap, within which two or more Different non-zero intensities can be generated when many spots 90 overlap completely or partially.

  In one embodiment, the spot 90 is square or rectangular so that a rectangular light pattern can be generated that has (at least approximately) one non-zero intensity between adjacent spots and no gaps. Has a geometric shape.

  This is illustrated in FIG. 6 which is a top view on the optical integrator 72 showing an array of 7 · 7 first microlenses 88. The boundaries of the first microlenses 88 form a regular grid of squares that can be individually illuminated with different or equal light patterns. In the configuration shown in FIG. 6, it is assumed that only the light incident facet 92 located in the two poles P1 and P2 surrounded by the thick solid line is illuminated. The poles P1 and P2 are symmetrically arranged on the opposite side of the optical integrator 72 and are substantially T-shaped.

  In contrast to the prior art scheme, the poles P1, P2 are not completely illuminated, but are illuminated with a rectangular light pattern LP that is evenly repeated on the light incident facets 92 of each first microlens 88. Furthermore, each light pattern 94 is knitted from square spots 90 arranged sequentially along the line. In this case, the aspect ratio of each light pattern 94 is 4: 1, and the longitudinal side extends along the X direction.

  As described above with reference to FIG. 5a, the above aspect ratio results in a field having the same 4: 1 aspect ratio illuminated in the intermediate field plane 80 (no anamorphic optical elements in between). Assuming). When the scanning direction of the projection exposure apparatus 10 coincides with the Y direction, the illumination of the optical integrator 72 shown in FIG. 6 has a short side extending along the scanning direction Y and a long side extending in the X direction. An illumination field 14 will result. Since only the light incident facets 92 within the poles P1, P2 are illuminated, the light should be incident on the intermediate field plane 80 with an inclination from the opposite side exclusively as characteristic in a dipole illumination setting. become.

  If the illumination field should be of half width with an aspect ratio of 2: 1 for example, the left and right spots in each light pattern LP so that the two intermediate positions are illuminated simultaneously by the two spots 90 90 can be shifted with respect to the center. In this case, the illumination field in the intermediate field plane 80 (and in any subsequent field plane) will also have an aspect ratio of 2: 1, but no light will be occluded in the illumination system 12, or so Otherwise there is no loss, so it has twice the radiation power. If the radiant power should not be doubled, the left and right spots 90 are simply turned off (eg, moved away from the optical integrator 72). It should be noted that reducing the field size by changing the light pattern LP does not substantially change the angular distribution of light incident on the mask 16.

IV. Substitution of the field stop function In the illumination system 12 of the scanner-type projection exposure apparatus 10, the field stop 82 ensures a sharp edge (at least along the long side of the illumination field extending parallel to the scanning direction Y). In addition, the length of the illumination visual field 14 along the scanning direction Y is increased or decreased at each of the start and end of the scanning process. This opening and shutting function is required to ensure that all points on the mask receive the same amount of light energy. For this purpose, a blade is usually provided that can be moved along the scanning direction Y.

  In the illumination system 12, the geometric shape of the visual field can be changed by changing the light pattern illuminated on the light incident facet 92 of the optical integrator 72. Thus, at least in principle, there is no need for such an adjustable field stop 82. Without the field stop 82, the field stop objective 84 can also be omitted, resulting in a very significant simplification of the overall design of the illumination system 12. Although having a field stop objective 84, it simply has a field stop 82, eg, a stop that forms the boundary of only the longitudinal edge of the illumination field 14, while the vertical edge is solely determined by the illumination of the optical integrator 72. It is also possible.

  If the field stop 82 and the field stop objective 84 are to be omitted, the opening and blocking functions must be delegated to the remaining components of the illumination system 12, in particular the mirror array 46 and its controller 50.

1. First Technique One technique for providing the above-described surrogate is described below with reference to FIGS. 7-9 showing different light patterns on the light incident facet 92 of a single first microlens 88. FIG. 7 shows an instantaneous light pattern LP in which the illumination field 14 has the maximum spread along the scanning direction Y at the midpoint of the scanning process. The light pattern LP has a rectangular geometric shape having an aspect ratio corresponding to the aspect ratio of the illumination field 14 on the mask 16 as described above. The rectangular light pattern LP is knitted from _n spot rows R _{1 to} R _n , and each row is knitted from a plurality of spots 90 arranged sequentially along a line parallel to the X direction.

At the start of the scanning process, only the line R ₁ is illuminated over a time interval T during which N light pulses are generated by the light source 30. This is shown in the left diagram of FIG.

Next, the second row R ₂ is further illuminated over a time interval T until another N light pulses are incident on the mask 16, see the middle diagram of FIG. This situation corresponds to the situation in which the field stop 82 starts to open at the start of the scanning process in the conventional illumination system. The step of gradually turning on more rows R _i illuminates all n rows R ₁ to R _{n of the} light pattern LP shown in FIG. 7, as shown in the right diagram of FIG. Will continue until. This corresponds to a situation where the field stop 82 is fully opened in the conventional illumination system.

The scanning process is then continued without modifying the light pattern. Next, the above-described process is followed in reverse, i.e., only the last row R _n is the beginning at the first line R ₁ 1 by one-off until illuminated, this right drawing of FIG. 9 Please refer. The scanning process ends when the last row Rn is turned off.

The light incident facets 92 of the remaining microlenses 88 can be illuminated in the same manner as described above with reference to FIGS. Each of the rows R ₁ to R _n receives the same number N of light pulses when these rows are turned on or off, so that each point on the mask 16 has exactly the same number of light during the entire scanning process. Guaranteed to receive a pulse. Accordingly, the light source 30 must be synchronized with the mirror controller 50 to ensure that the above-described conditions regarding the number of light pulses are met.

On or off of rows R ₁ to R _n , either the spot that is turned on or off is either directed to the desired location or to the light absorbing surface outside the optical integrator 72, respectively. As can be easily achieved by setting the deflection angle in the corresponding mirror element M _ij . If spot 90 is to be turned on or off, it is necessary to move the spot across the light entrance facet of optical integrator 72. In order to avoid undesired perturbations, the spot 90 must be moved during the interval between successive light pulses. This movement requires a very quick movement of the mirror element M _ij .

2. Second Approach Such a rapid movement of the spot 90 over a long distance does not turn the spot 90 completely on or off, but continuously over the light incident facet 92 of a single first microlens 88. It can be avoided when moved.

  This method will be described below with reference to FIGS.

  FIG. 10 is a top view on the light incident facets 92a, 92b, 92c of three adjacent microlenses 88. FIG. Light shielding face pairs 96a, 96b, and 96c are fixed to the light incident facets 92a, 92b, and 92c so that central stripes having different heights along the scanning direction Y remain uncovered. In this embodiment, the light shield pairs 96a, 96b, 96c are sized so that the uncovered stripe at the center is not restricted in the X direction but only along the Y direction.

  For the purpose of simplification, a light shield 96a is provided in one third of the light incident facet 92 of the optical integrator 72, a light shield 96a is provided in the third, and a light shield 96c is provided in the remaining third. It is assumed that it is provided.

  FIG. 11a schematically illustrates the intensity distribution obtained in the intermediate field plane 80 when the same number of three types of light incident facets 92a, 92b, 92c are illuminated. The intensity profile along the Y direction increases until reaching the top and then decreases again. This intensity profile approximates a trapezoidal intensity profile along the scanning direction Y. This approximation improves as the number of different light shields 96a, 96b, 96c increases. The height and inclination of the trapezoidal intensity profile are mainly determined by the distribution of the light shields 96a, 96b, 96c.

  At the beginning and end of the scanning process, the intensity profile along the scanning direction Y should be modified. FIGS. 11b, 11c and 11d show how the intensity profile shown in FIG. 11a is gradually trimmed from the right side. The trimming process starts by moving the spot 90 along the scanning direction Y on the light incident facet 92c covered with the light shield 96c. In this case, the row of spots 90 that are initially adjacent to one of the light shields 96c will be completely shielded by this light shield, which is shown by the white square 90 'in FIG. 11b. Yes. This process is repeated, but this time the spot 90 illuminated on the light incident facet 92b provided with the light shield 96b is also moved in the same direction. As a result, the row of spots 90 ″ is similarly shielded by one of the light shields 96 b. This situation is illustrated in FIG. 11c.

  When the highest level of the intensity profile is reached, the spot 90 on the light incident facet 92a provided with the light shield 96a is also moved along the scanning direction Y. As a result, the row of spots 90 '' 'is similarly shielded by one of the light shields 96a. This situation is illustrated in FIG. At the start of the scanning process, this process must be repeated in reverse order from the opposite side.

  The light entrance facets 92a, 92b, 92c, respectively covered by different pairs of light shields 96a, 96b, and 96c, are distributed over the entrance surface of the optical integrator 72 so that adverse effects on the intensity distribution in the pupil plane 70 are minimized. There must be. Without such an optimized distribution, the illumination angle distribution corresponding to the light intensity distribution in the pupil plane 70 changes as the spot 90 is moved along the scanning direction Y during the start and end of the scanning process. May occur.

  FIGS. 12 a to 12 c illustrate the above-described principle in a dipole illumination setting in which two poles P 1 and P 2 are illuminated on the light entrance facet of the optical integrator 72. At the start and end of the scanning process, only the light incident facet 92c provided with the light shield 96c contributes to the illumination of the mask 16. As the scanning process continues, the light incident facet 92b provided with the light shield 96b also contributes to the illumination of the mask 16, see FIG. 12b. Finally, the light incident facet 92a provided with the light shield 96a contributes to the illumination of the mask 16 as well, see FIG. 12c.

  As can be seen in FIGS. 12a to 12c, different types of light incident facets 92a, 92b, 92c have different intensities in the poles P1, P2 when these different types of light incident facets 92a, 92b, 92c are turned on and off. It is distributed over the poles P1 and P2 so as not to greatly affect the balance. Such a balance cannot be obtained when different types of light incident facets are arranged along three lines extending from top to bottom in each of FIGS. 12a to 12c.

  This technique can be combined with the first technique as required. In this case, a trapezoidal or any other non-rectangular intensity profile of the illumination field 14 can be obtained along the scanning direction Y, and can be obtained without using the light shield pairs 96a, 96b, 96c. In this case, the row of spots 90 to be turned off does not move to the light shield, but is turned off by moving the spots to the absorption surface outside the optical integrator 72. It is only necessary to ensure that the time interval between two successive light pulses is sufficient to move the spot 90 to the absorbing surface.

3. Third Method It is also possible to omit only the field stop objective 84 while using a movable stop blade at another position in the illumination system 12. This is shown schematically in FIG. 13, which is an excerpted view of FIG. 2, showing a mirror array 46, a first condenser 58, and an optical integrator 72 having a first microlens 88 and a second microlens 94.

The solid line indicates the light LM ₁ emitted from the first micro-mirror M _ij of the row RM ₁ of the micro-mirrors M _ij. The micro mirror M _{ij in} the first row RM ₁ is controlled so as to illuminate only the upper part of the light incident facet 92 of the first micro lens 88 of the optical integrator 72. As a result, the light beam LM ₁ illuminates a portion of the field of view 14 on the mask 16 that is closest to one of its edges.

A broken line indicates the light beam LM ₅ emitted from the micromirror M _ij in the central row RM ₅ of the mirror array 46. The micro mirror M _ij in the central row RM ₅ is controlled so that the light beam LM ₅ illuminates only the central portion of the light incident facet 92 of the first micro lens 88. As a result, the light beam LM ₅ illuminates a line that traverses the center of the field of view 14 illuminated on the mask 16.

Dotted line indicates rays LM ₉ emitted from the micro-mirror M _ij of the last row RM ₉ of the micro-mirrors M _ij. The micromirror M _ij in the final row RM ₉ is controlled so that the light beam LM ₉ illuminates only the lower part of the light incident facet 92 of the first microlens 88. As a result, the light beam LM ₉ illuminates the closest portion of the field 14 illuminated on the mask 16 at the edge located opposite the edge illuminated by the light beam LM ₁ .

In the immediate vicinity of the micromirror array 46, an opaque blade 98 is arranged so that it can be moved along the scanning direction Y using the actuator 100 during the scanning process. As indicated by arrows in FIG. 13, when the blade 98 begins to move downward, the blade 98, light LM initially emitted from the first micro-mirror M _ij of the row RM ₁ of the micro-mirror M _{ij 1} will be shaded. As a result, the field of view 14 illuminated on the mask 16 is trimmed from the Y direction. The blade 98 will then block the light rays emanating from the adjacent row RM ₂ of the micromirror M _ij , thereby causing further trimming of the illumination field 14 and so on.

If the blade 98 continues to move until it reaches the central row RM ₅ , the field of view 14 illuminated on the mask 16 will have only half of its original length along the scanning direction Y.

Therefore, by the mirror elements M _ij that illuminates some parts of the light entrance facets 92 of the first microlenses 88 selected appropriately, to shield the mirror elements M _ij using opaque blade or another diaphragm The geometry of the field of view 14 illuminated on the mask 16 can be changed.

V. Method of Operation FIG. 14 is a flowchart illustrating the main steps of a method of operating an illumination system of a microlithographic projection exposure apparatus according to the present invention.

  In the first stage S1, the illumination system 12 of the microlithographic projection exposure apparatus 10 is prepared. The illumination system 12 includes an optical raster element 72 having a plurality of light incident facets 92.

  In step S 2, a light pattern organized from the individual spots 90 is generated on the light incident facets 92 of the optical raster element 72.

  In step S3, it is determined that the geometry of the field of view 14 illuminated in the mask plane 86 should be changed. The reason for making the above determination can be a change in the mask 16 or a change in the scanning process that requires opening and shutting off the illumination field 14 at the beginning and end of the scanning process, respectively.

  Next, the light pattern on the light incident facets 92 is altered by rearranging and / or removing and / or adding spots as described above.

  The above description of the preferred embodiments has been provided as an example. From the disclosure provided, those skilled in the art will not only understand the invention and its attendant advantages, but will also find apparent various variations and modifications to the disclosed structures and methods. Accordingly, applicants are urged to cover all such variations and modifications as fall within the spirit and scope of the invention as defined by the appended claims and equivalents thereof.

72 Optical raster element 90 Spot 92 Light incident facet LP Light pattern

Claims (17)

An illumination system of a microlithographic projection exposure apparatus (10),
a) a primary light source (30);
b) the system pupil plane (70);
c) a mask plane (86) in which an illuminated mask (16) can be placed;
d) a plurality of light incidents configured to generate a plurality of secondary light sources (95) located on the system pupil plane (70), each associated with one of the secondary light sources (95); An optical raster element (72) having facets (92);
e) including a beam deflection element (46) of a reflective or transmissive beam deflection element (M _ij ), each beam deflection element (M _ij ) having a deflection angle generated by the beam deflection element (M _ij ). A beam deflection device configured to illuminate a spot (90) on one of the light incident facets (92) at a position that is variable by changing;
f) The beam deflection element (M _ij ) so that a variable light pattern (LP) knitted from the spot (80) can be formed on at least one of the plurality of light incident facets (92). A control unit (50) configured to control
An illumination system comprising: The spot (90) illuminated by the beam deflection element (M _ij ) is at least 5 times, preferably at least 10 times, more preferably, the largest total area of any of the light incident facets (92). 2. The illumination system of claim 1, having a total area that is at least 20 times smaller.   3. Illumination system according to claim 1 or 2, characterized in that the spot (90) has at least a substantially rectangular geometric shape.   4. Illumination system according to any one of claims 1 to 3, characterized in that the light patterns generated on all light incident facets (92) are identical at a given moment. The control unit (50) is configured such that the length of the light pattern (LP) along the scanning direction (Y) is gradually changed during the scanning process of the device (10), and perpendicular to the scanning direction. 5. The beam deflecting element ( _Mij ) is configured to control the beam deflection element ( _Mij ) so that the length of the light pattern along a direction remains constant. The illumination system described in 1. The control unit (50) is configured to control the beam deflection element (M _ij ) so that the light pattern has a different length along the scanning direction (Y) at a given moment. The illumination system according to claim 5, characterized in that:   The light-shielding body (96a, 96b, 96c) is provided in at least one part of the said light-incident facet (92a, 92b, 92c), The any one of Claims 1-6 characterized by the above-mentioned. The illumination system described.   At least one light incident facet (92a, 92b, 92c) is provided with a pair of light shields (926, 96b, 96c) disposed on opposite sides of the light incident facet (92a, 92b, 92c). The illumination system according to claim 7.   A diaphragm (98) disposed in the immediate vicinity of the beam deflection device; and an actuator (100) for moving the diaphragm parallel to the scanning direction (Y) of the microlithographic projection exposure apparatus (10). The illumination system according to any one of claims 1 to 8, characterized in that: An illumination system of a microlithographic projection exposure apparatus (10),
a) system pupil plane (70);
b) An array of refractive or diffractive microelements (88), each microelement (88) having a light entrance facet (92) and a secondary light source (95) on the system pupil plane (70) An optical raster element (72) for generating
c) including a beam deflection array (46) of reflective or transmissive beam deflection elements (M _ij ), each beam deflection element being modified by changing the deflection angle produced by the beam deflection element. A beam deflection device configured to illuminate a spot (90) on the optical raster element (72) in a possible position;
Including
The spot (90) generated by at least one of the beam deflection elements (M _ij ) is at least 5 times, preferably at least 10 times the largest area of any of the light incident facets (92). Having a total area that is twice, more preferably at least 20 times smaller,
An illumination system characterized by that. A method for operating an illumination system of a microlithographic projection exposure apparatus, comprising:
a) preparing an illumination system (12) of a microlithographic projection exposure apparatus (10) including an optical raster element (72) having a plurality of light incident facets (92) in the illumination system (12) (S1);
b) generating a light pattern (LP) organized from individual spots (90) on the light incident facets (92) of the optical raster element (72) (S2);
c) determining that the geometry of the field of view (14) illuminated in the mask plane (86) should be changed;
d) changing the light pattern (LP) on the light incident facet (92) by rearranging and / or removing and / or adding spots (90);
A method comprising the steps of: The optical raster element (72) includes refractive or diffractive microelements (88);
Each microelement (88) is associated with one light incident facet (92),
The method according to claim 11. Said illumination system provided in step a) comprises a beam deflection device comprising a beam deflection array (46) of reflective or transmissive beam deflection elements (M _ij );
The light pattern (LP) is changed by changing the deflection angle generated by the beam deflection element (M _ij ),
13. A method according to claim 11 or claim 12 characterized in that.   The spot (90) has a total area that is at least 5 times, preferably at least 10 times, more preferably at least 20 times smaller than the largest total area of any of the light incident facets (92). The method according to any one of claims 11 to 13.   15. A method according to any one of claims 11 to 14, characterized in that a two-dimensional array of spots (90) is illuminated on each light incident facet (92). Method according to claim 15, characterized in that the rows (R _i ) of spots (90) are illuminated simultaneously or darkened again.   A diaphragm (98) arranged in the immediate vicinity of the beam deflection device is at least relative to the optical axis (OA) of the illumination system (12) along the scanning direction (Y) of the microlithographic projection exposure apparatus (10). 14. The method of claim 13, wherein the method is moved substantially vertically.

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